Definitions of vocabulary terms related to tornadoes

Tuesday

May 8, 2007 at 12:01 AMMay 8, 2007 at 8:19 AM

We've put together a list of terms related to "tornadoes" to help you when writing your stories.

Jean Hodges, National Editor

• Tornado — A violently rotating column of air, usually pendant to a cumulonimbus, with circulation reaching the ground. It nearly always starts as a funnel cloud and may be accompanied by a loud roaring noise. On a local scale, it is the most destructive of all atmospheric phenomena.

• Multiple Vortex Tornado — A tornado in which two or more condensation funnels or debris clouds are present at the same time, often rotating about a common center or about each other. Multiple-vortex tornadoes can be especially damaging.

• Wedge Tornado — Slang for a large tornado with a condensation funnel that is at least as wide at the ground as it is tall from the ground to cloud base. The term "wedge" often is used somewhat loosely to describe any large tornado. However, not every large tornado is a wedge. A true wedge tornado, with a funnel at least as wide at the ground as it is tall, is very rare.

• Wall Cloud — A localized, persistent, often abrupt lowering from a rain-free base. Wall clouds can range from a fraction of a mile up to nearly five miles in diameter, and normally are found on the south or southwest (inflow) side of the thunderstorm. When seen from within several miles, many wall clouds exhibit rapid upward motion and cyclonic rotation.

However, not all wall clouds rotate. Rotating wall clouds usually develop before strong or violent tornadoes, by anywhere from a few minutes up to nearly an hour. Wall clouds should be monitored visually for signs of persistent, sustained rotation and/or rapid vertical motion.

• Funnel Cloud — A condensation funnel extending from the base of a towering cumulus or Cb, associated with a rotating column of air that is not in contact with the ground (and hence different from a tornado). A condensation funnel is a tornado, not a funnel cloud, if either a) it is in contact with the ground or b) a debris cloud or dust whirl is visible beneath it.

• Downdraft — Small-scale downward moving air current in a cumulonimbus cloud.

• Hook Echo — A radar reflectivity pattern characterized by a hook-shaped extension of a thunderstorm echo, usually in the right-rear part of the storm (relative to its direction of motion). A hook often is associated with a mesocyclone, and indicates favorable conditions for tornado development.

• Cyclone — (abbrev. CYC) - A large-scale circulation of winds around a central region of low atmospheric pressure, counterclockwise in the Northern Hemisphere, clockwise in the Southern Hemisphere.

• Mesocyclone — (abbrev. MESO)- A storm-scale region of rotation, typically around 2-6 miles in diameter and often found in the right rear flank of a supercell (or often on the eastern, or front, flank of an HP storm). The circulation of a mesocyclone covers an area much larger than the tornado that may develop within it. Properly used, mesocyclone is a radar term; it is defined as a rotation signature appearing on Doppler radar that meets specific criteria for magnitude, vertical depth, and duration. It will appear as a yellow solid circle on the Doppler velocity products. Therefore, a mesocyclone should not be considered a visually-observable phenomenon (although visual evidence of rotation, such as curved inflow bands, may imply the presence of a mesocyclone).

• Supercell — Short reference to Supercell Thunderstorm; potentially the most dangerous of the convective storm types. Storms possessing this structure have been observed to generate the vast majority of long-lived strong and violent (F2-F5) tornadoes, as well as downburst damage and large hail. It is defined as a thunderstorm consisting of one quasi-steady to rotating updraft which may exist for several hours.

• Doppler Radar — Radar that can measure radial velocity, the instantaneous component of motion parallel to the radar beam (i.e., toward or away from the radar antenna).

• Tornado Alley — A term often used by the media to denote a zone in the Great Plains region of the central United States, often a north–south oriented region centered on north Texas, Oklahoma, Kansas, and Nebraska, where tornadoes are most frequent.

Affiliated Delaware Papers

Original content available for non-commercial use under a Creative Commons license, except where noted.
Smyrna/Clayton Sun-Times ~ 24 W. Main St., Middletown, DE 19709 ~ Privacy Policy ~ Terms Of Service